1. Field of the Invention
The invention relates to a method and system for increasing the efficiency and productivity of a high temperature furnace, and more particularly, the invention relates to a device and method for operating air-fuel-fired burners in a furnace with oxygen enrichment for reducing Nitrous oxide emissions, increasing thermal efficiency, and improving productivity.
2. Brief Description of the Related Art
In known regenerative furnaces burner blocks having multiple firing ports are positioned on opposite sides or ends of the furnace combustion chamber. Each of the firing ports contains one or more burners for delivery of fuel into the combustion chamber. The firing ports also provide a combustion air supply around the burners. During furnace operation, the burners on opposite sides of the combustion chamber are operated alternately in a cyclic fashion. While the burners on one side of the combustion chamber are fired, cooling air is delivered to the opposite side of the combustion chamber. This cooling air is delivered through central lances positioned in each of the burners.
Regenerative furnaces have regenerators or refractory checkers on either side of the furnace. The regenerator checkers provide a heat transfer medium to transfer heat from the hot combustion gases exiting the combustion chamber to the cold combustion air which is delivered to the furnace. The regenerator checkers are heated to a high temperature by the hot exhaust gases at about 2900.degree. F. to about 3000.degree. F. which are passed from the top of the checkers to the bottom of the checkers at the exhaust side of the furnace for a cycle of approximately 20 minutes. During the next cycle, the combustion air being delivered to the furnace at ambient temperature is passes from the bottom of the preheated checker to the top of the checker for heat extraction. The combustion air is preheated to a temperature of about 2300.degree. F. to about 2400.degree. F. by the regenerator checker before it is delivered to the combustion chamber of the furnace. The combustion air and exhaust gas flows are reversed typically every 20 minutes so that each side checker can be alternately heated and used for preheating of combustion air.
Thermal efficiency of the regenerative furnaces may suffer due to an insufficient oxygen supply from a variety of causes. Insufficient oxygen supply may be caused by regenerator plugging, cracks in the regenerator, or other regenerator failure. Furnace efficiency can be improved in several different ways such as: 1) by installation of additional oxygen lances either under each of the burners or on one side of each of the burners; 2) by adding additional oxy-fuel burners to the sidewalls of the regenerative furnace; 3) by adding additional oxygen to the combustion air delivered to the firing ports, termed global oxygen enrichment; or 4) replacement of some of the fuel lances within dual fuel burners with additional oxygen lances.
However these solutions to insufficient oxygen supply all have substantial drawbacks. For example, it is often difficult to install additional oxygen lances or oxy-fuel burners in the furnace due to design or space constraints. The spaces where burners or lances can be placed are defined by burner geometry and improper placement can lead to quality problems, crown overheating, or regenerator hot spots that can dramatically reduce the useful life of the furnace. Often there is insufficient space for drilling holes for installation of the additional lances or burners at the desired locations beside or below the firing ports. In addition, refractory core drilling or refractory block removal to allow installation of the additional lances or burners can be physically impossible or at least very costly.
Global oxygen enrichment to improve efficiency is not an efficient solution in all circumstances. Often oxygen enrichment is required towards the end of the furnace life when the regenerators are plugged or severely damaged and are no longer delivering sufficient combustion oxygen even with oxygen enrichment of the combustion air. In most cases, additional heat is required in damaged areas where it is not possible to get the needed excess oxygen through the regenerators. In many cases, due to the inability to get oxygen where heat is required or the loss of oxygen through refractory cracks, the oxygen enrichment technique is unacceptable.
Accordingly, it would be desirable to provide a simple and economical system for oxygen enrichment of a refractory furnace.